The present invention relates to elastomers. In particular, the present invention relates to an additive for improving the heat age properties of elastomers, including hardness, tensile strength, elongation, and modulus.
Elastomer compositions are known in the art. For example, heat-cured elastomers, particularly silicone elastomers, are very useful in high temperature sealing applications such as electrical wires and cables, automotive and oven gaskets, hot air ducts, window hoods, and the like. In these applications the heat age properties of the elastomer are of primary importance for optimal function. As used herein, "heat age properties" refers to the degree to which high or low temperature affects the elastomer's physical properties, including compression set, elongation, hardness, modulus, and tensile strength. For many applications significant changes in these properties with temperature or in response to temperature could result in failure of the material to meet the requisite performance specifications.
Heat age properties of silicone elastomers are generally dependent on at least three factors: the composition and quantity of the filler; the composition and quantity of any processing aids present in the formulation (processing aids affect the heat age properties of the elastomer by modulating the polymer-filler interactions), and the crosslink density or the state of cure of the polymer phase.
Heat age properties are particularly important in gasket and other sealing applications. Prior art attempts to improve silicon-based gasket materials have focused on improving compression set or sealing force retention. For example, U.S. Pat. No. 5,346,940 to Brassard et al. and U.S. Pat. No. 5,623,028 to Fitzgerald et al. disclose a method for controlling the sealing force retention. There are other examples in the literature describing heat age additives for silicone elastomers, e.g., TiO.sub.2, iron octoate, Ce(OH).sub.4 and rare earth octoates. Nonetheless, there remains a need in the art for methods for further improving the heat age properties of elastomers.